As an important transportation equipment for coal mining face, a scraper conveyer not only attains a function of loading and transporting the material, but also serves as a pushing fulcrum for the coal loading and operation track of the coal cutter and the hydraulic support. Therefore, whether the scraper conveyer operates reliably, safely and efficiently has direct influence on the production efficiency of downhole coal mining and the economic benefit and development of the coal mining enterprise.
As the conveying capacity of scraper conveyer is gradually increased and the laying length of scraper conveyer is greatly increased, the coal load borne on the scraper chains becomes higher and higher. The scraper chains are not absolutely rigid bodies; instead, the scraper chains are elongated elastically as the load on the chains is increased, and thereby result in a loose chain phenomenon. Since loose scraper chains may cause an off-chain, blocked chain, broken chain situation, etc., the production along the fully-mechanized mining face may be affected. Therefore, the scraper chains must be tensioned up in due course.
At present, there are mainly two chain tensioning methods in China: one is manual chain tensioning and the other one is hydraulic chain tensioning. Manual chain tensioning is to break the chains and remove several chains from the chains manually when the chains become loose obviously. This method is very inefficient and involves high labor intensity, and the machine has to be shut down before the manual chain tensioning process can be commenced. Consequently, the operation time of the machine is severely shortened, and the economic benefit is affected. Hydraulic chain tensioning is mainly to adjust the center distance between the chain wheels under the action of a hydraulic cylinder and thereby to achieve tension up of the scraper chains. Though the method can attain an automatic tensioning effect theoretically, the practical application result is not ideal, as hydraulic control elements may fail easily under harsh downhole conditions. In addition, that method involves high system cost, troublesome maintenance process and high maintenance cost. Therefore, the hydraulic chain tensioning method is not widely applied in medium-sized and small-sized coal mines.
Besides, since the coal conveyed on the scraper conveyer is unloaded by gravity at the head of the scraper conveyer, it is impossible to fully unload the coal, and the residual coal may remain at the corners of the scraper or along the middle chute. The residual coal on the scraper aggravates the wearing of the scraper conveyer on one hand, and increases the operation burden on the equipment on the other hand. Consequently, the scraper conveyer does more idle work and its efficiency is severely decreased. The residual coal may even enter into the chain wheels and results in a chain jumping, chain breaking accident.